U.S. patent number 10,317,422 [Application Number 15/553,563] was granted by the patent office on 2019-06-11 for multi-directional fluid velocity measurement device (fvmd).
This patent grant is currently assigned to Technological University of Dublin. The grantee listed for this patent is Dublin Institute of Technology. Invention is credited to Brian Kearney, Derek Kearney.
United States Patent |
10,317,422 |
Kearney , et al. |
June 11, 2019 |
**Please see images for:
( Certificate of Correction ) ** |
Multi-directional fluid velocity measurement device (FVMD)
Abstract
This present application relates generally to the science of
fluid flow measurement and provides a multi-directional fluid
velocity measurement device (FVMD) employing a plurality of pitot
tubes arranged in a 3D configuration and extending from a spherical
main body in which measurement sensors are provided.
Inventors: |
Kearney; Derek (Walkinstown,
IE), Kearney; Brian (Dublin, IE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Dublin Institute of Technology |
Dublin |
N/A |
IE |
|
|
Assignee: |
Technological University of
Dublin (Dublin, IE)
|
Family
ID: |
52822165 |
Appl.
No.: |
15/553,563 |
Filed: |
February 19, 2016 |
PCT
Filed: |
February 19, 2016 |
PCT No.: |
PCT/EP2016/053566 |
371(c)(1),(2),(4) Date: |
August 24, 2017 |
PCT
Pub. No.: |
WO2016/135061 |
PCT
Pub. Date: |
September 01, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180045751 A1 |
Feb 15, 2018 |
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Foreign Application Priority Data
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Feb 25, 2015 [GB] |
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1503149.5 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01P
5/165 (20130101) |
Current International
Class: |
G01P
5/165 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1367389 |
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Sep 2002 |
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CN |
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202075303 |
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May 2011 |
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CN |
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102298072 |
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Dec 2011 |
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CN |
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0947809 |
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Oct 1999 |
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EP |
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2007/042803 |
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Apr 2007 |
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WO |
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WO 2007/042803 |
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Apr 2007 |
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WO |
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Other References
Search Report under Section 17(5), dated Jan. 21, 2013,
Intellectual Property Office, Great Britain. cited by applicant
.
International Standard, IEC 61400-12-1, First Edition, Dec. 2005,
Wind Turbines, Part 12-1: Power performance measurements of
electricity producing wind turbines. cited by applicant .
Eckman, et al., "A Pressure-Sphere Anemometer fr Measuring
Turbulence and Fluxes in Hurricanes", Journal of Atmospheric and
Oceanic Technology, vol. 24, Oct. 18, 2006. cited by applicant
.
Friis Pedersen, Troels, "Development of a Classification System for
a Cup Anemometers--CLASSCUP", Riso National Laboratory, Roskilde,
RISO-R-1348 (EN), Apr. 2004. cited by applicant .
Kadygrov, E.N., "Integrated Profiling Systems and Other Upper-Air
Measurement Techniques", World Meteorological Organization, Nov.
16, 2005. cited by applicant .
International Search and Written Opinion, dated Apr. 14, 2016, WO.
cited by applicant.
|
Primary Examiner: Dowtin; Jewel V
Attorney, Agent or Firm: Holzer Patel Drennan
Claims
The invention claimed is:
1. A multi-directional fluid velocity measurement device for
measuring three dimensional characteristics of fluid flow, the
device comprising: a main body having a substantially spherical
outer surface; a support for supporting the main body; a plurality
of Pitot tubes, each of the Pitot tubes extending outwardly from a
proximal end at the main body to a distal end; a plurality of
pressure sensors, arranged within the main body, each pressure
sensor being in fluid communication with a respective one of the
Pitot tubes, wherein the Pitot tubes are distributed about the
outer surface in three dimensions wherein the distal end of each
Pitot tube is a sufficient distance from the outer surface of the
main body such that the pressure readings taken by the Pitot tubes
are not substantially corrupted by the localized pressure
variations created by the wind flowing over the main body; and a
plurality of sockets arranged about the main body, wherein each
socket is in fluid communication with a pressure sensor and where
the Pitot tubes are removably engageable with the sockets.
2. A device according to claim 1, wherein the sufficient distance
is at least the radius of the main body.
3. A device according to claim 2, wherein the sufficient distance
is between twice and ten times the radius of the main body.
4. A device according to claim 1, wherein the removable engagement
is such that a Pitot tube may be removed by hand.
5. A device according to claim 4, wherein the removable engagement
comprises the use of screw fit connection, push-fit connection or a
push and twist fit connection.
6. A device according to claim 1, wherein the pitot tubes and
socket are shaped to present a continuous curved surface at the
pitot tube-socket interface to minimise disruption to airflow.
7. A device according to claim 1, wherein a heating element is
provided on each Pitot tube to prevent icing.
8. A device according to claim 1, further comprising at least one
additional sensor, wherein the at least one additional sensor
comprises one or more of the following: a) a temperature sensor; b)
b) a humidity sensor; c) c) a barometric pressure sensor; and d) d)
a rainfall sensor.
9. A device according to claim 1, wherein the main body comprises
two hemi-spheres which are removably connected to one and
other.
10. A device according to claim 9, wherein a seal is provided
between the two hemi-spheres.
11. A device according to claim 1, wherein the number of Pitot
tubes is more than required to provide measurement of fluid flow in
three dimensions.
12. A device according to claim 11, wherein the number of Pitot
tubes is 64.
13. A multi-directional fluid velocity measurement device for
measuring three dimensional characteristics of fluid flow, the
device comprising: a main body having a substantially spherical
outer surface; a support for supporting the main body; a plurality
of Pitot tubes, each of the Pitot tubes extending outwardly from a
proximal end at the main body to a distal end; a plurality of
pressure sensors, arranged within the main body, each pressure
sensor being in fluid communication with a respective one of the
Pitot tubes, wherein the Pitot tubes are distributed about the
outer surface in three dimensions wherein the distal end of each
Pitot tube is a sufficient distance from the outer surface of the
main body such that the pressure readings taken by the Pitot tubes
are not substantially corrupted by the localized pressure
variations created by the wind flowing over the main body; and a
data recorder for recording data obtained from each of the pressure
sensors, wherein the data recorder is housed within the main
body.
14. A device according to claim 13, wherein the sufficient distance
is at least the radius of the main body.
15. A device according to claim 14, wherein the sufficient distance
is between twice and ten times the radius of the main body.
16. A device according to claim 13, further comprising a power
source for powering the data recorder, wherein said power source is
also housed within the main body.
17. A multi-directional fluid velocity measurement device for
measuring three dimensional characteristics of fluid flow, the
device comprising: a main body having a substantially spherical
outer surface; a support for supporting the main body; a plurality
of Pitot tubes, each of the Pitot tubes extending outwardly from a
proximal end at the main body to a distal end; a plurality of
pressure sensors, arranged within the main body, each pressure
sensor being in fluid communication with a respective one of the
Pitot tubes, wherein the Pitot tubes are distributed about the
outer surface in three dimensions wherein the distal end of each
Pitot tube is a sufficient distance from the outer surface of the
main body such that the pressure readings taken by the Pitot tubes
are not substantially corrupted by the localized pressure
variations created by the wind flowing over the main body; and a
connector defined in the main body for removably engaging with the
support.
18. A device according to claim 17, wherein the sufficient distance
is at least the radius of the main body.
19. A device according to claim 18, wherein the sufficient distance
is between twice and ten times the radius of the main body.
Description
FIELD OF THE APPLICATION
This application relates generally to the science of fluid flow
measurement and, more particularly provides a multi-directional
fluid velocity measurement device (FVMD).
BACKGROUND TO THE APPLICATION
Accurate wind measurements are essential in various applications
and for various industries. In the wind industry, the
miscalculation of wind resources for electricity generation is an
industry wide problem. Industry estimates suggest that wind
developers are inaccurately predicting the pre-construction energy
yield estimates of wind farms by ten percent on average globally:
Site selection is the first crucial step in the practical
development of these farms and investors decide whether or not to
invest on the basis of wind resource assessment reports. Typically,
these reports require a rigorous assessment of site-specific wind
conditions over a twelve-month period before any significant
investment proceeds. Industry experts suggest that existing wind
measurement technology is not up to the task of providing
sufficient data for an accurate assessment of a site's wind
resource potential. A second problem identified is with the ongoing
operation of so-called horizontal axis wind turbines (HAWT) once
installed. Misalignment of the yaw angle of a HAWT with the
incident wind is apt to cause significant variation in power output
(as well as inducing additional stress loads on the critical
components of the turbines causing premature wear and tear and
accelerating the maintenance cycle). For example, a yaw angle
misalignment of .+-.15.degree. will lead to a 5-6% annual energy
loss. Turbine misalignment is a common phenomenon particularly in
lower wind speed conditions where yaw angle misalignments of up to
30% are common across the industry.
These problems are exacerbated when HAWTs are located in complex
terrains. Trials conducted in Warwick have shown that the likely or
predicted energy output from building-mounted micro-wind turbines
are prone to overestimation by factors of between 15 and 17.
Current approaches to addressing the problems of wind resource
measurement may be generally categorized into discreet families of
devices as follows: Mechanical anemometry (cup and vane); active
remote sensing technology (SoDAR and LiDAR); hot-wire anemometry;
sonic anemometry, and; pitot-tube anemometry and subdivisions
thereof.
PRIOR ART APPROACHES
Mechanical anemometry: Cup anemometers and wind vanes dominate in
wind energy measurement applications. The former, though varying in
size, cup-shape and arm-length usually comprise some configuration
of three cups arranged (coplanar) on a horizontal plane such that
they ideally rotate around a vertical shaft at a speed proportional
to the horizontal speed component of the incident wind. Wind vanes
are used to indicate wind direction and typically comprise an
asymmetrical marker-vane which is free to rotate about a vertical
axis over the entire (azimuthal) 360.degree. degree range so that
it assumes a direction parallel to the direction of the mean wind
flow. Data from the latter are used by the industry to facilitate
the optimum alignment of the turbine blades to the incident wind.
Typically, mechanical rotating anemometers generate an analogue
output signal by means of a so-called reed switch or through the
pole interaction of a magnet to a coil.
The International Electrotechnical Commission (IEC) Standard
61400-12-1:2006, relating to wind turbines, exclusively prescribes
the use of cup anemometers and wind vanes to gather the data
necessary for the calculation of power performance measurements of
electricity producing wind turbines. In other words, the power
curve gives the predicted wind turbine power production estimate
for a particular wind speed. According to this standard, the power
characteristics of an HAWT are determined by the measured power
curve and the estimated annual energy production (AEP)--See IEC
61400-12-1: 2006 Wind Turbines--Part 12-1: Power performance
measurements of electricity producing wind turbines (pp. 7). The
measured power curve is determined by ` . . . collecting
simultaneous measurements of wind speed and power output at the
test site for a period that is long enough to establish a
statistically significant database over a range of wind speeds and
under varying wind and atmospheric conditions. The AEP is
calculated by applying the measured power curve to reference wind
speed frequency distributions, assuming 100% availability` (p.
7).
Although the cup anemometer has long been considered a robust and
suitable instrument for wind speed testing, international standards
authorities and industry experts are becoming ever more aware of
the technical limitations of using this instrument as a speed
measurement device. Users of the IEC standard (see above) are
cautioned to be aware of the large differences that arise from
variations caused by wind shear and turbulence. Optimally, cup
anemometers are designed to measure the direct, incoming homogenous
laminar wind flow and thus, field flow conditions associated with
fluctuating wind vectors, both in magnitude and direction will
cause different instruments to perform differently in the same
conditions (P. 7).
The technology has recently come under close scrutiny from the wind
industry where multi-million euro investments are based on the
so-called "bankable datasets" derived from traditional cup
anemometer readings. The issue that arises is that small errors in
wind speed measurement are apt to translate into much larger
deviations in the predicted power output of an HAWT. The EU funded
wind trial project SitePariden (2001) discovered that average wind
speeds measured with different cup anemometer types--including
pre-calibrated instruments--deviated by up to 7% points relative to
each other. The effect of these observed differences on the
estimated wind energy production is not trivial and could account
for a 10% miscalculation of the resource in reasonable wind regimes
of nine meters per second and up to 20% in sites with mean wind
speeds of less than five meters per second.
As well as differences between cup anemometers, a number of
inherent design limitations have been identified. Firstly, the
CLASSCUP project has shown that cup anemometers have significant
difficulties with producing accurate readings in angled or off-axis
flow conditions when the flow exceeds 15 degrees in either a
negative or positive direction [Friis Pedersen, T., Riso National
Lab, Roskilde (DK)--Wind Energy Department, 2003--Development of a
classification system for cup anemometers--CLASSCUP].
Secondly, aerodynamic over-speeding (a known behavioural
response-effect commensurate with the friction-bearing
characteristics of the instrument) has been identified as a
potential source of bias in wind speed data, especially in high or
fluctuating wind conditions. Thirdly, industry sources have
identified a self-excited vibratory phenomenon termed dry friction
whip (DFW) whereby affected anemometers can report wind speeds
lower than true speeds by up to several percent.
Finally, and because cup anemometers and wind vanes are,
essentially, rotating mechanical devices, there are several
external parameters known to have a deleterious effect on
rotational function: inter alia, the effect on the rotating
instrument's friction bearings due to extreme temperature
variations; the stalling effect of heavy snow; and, the effect on
rotatory function due to the accretion of ice and rime in cold
weather. Human error may also play a part in yaw misalignment of
HAWTs as a wind vane need only be misplaced by a few millimeters in
order to induce a major misalignment. For example, a 5 to 6
millimeters turn of some wind vanes induces a 15.degree. yaw
misalignment causing a 5 to 6% annual energy loss. These are
significant problems for the wind energy sector not least because
minimal errors in wind speed measurement lead to significant error
accumulation in all subsequent calculations based on these core
measurements (according to Betz's Law the power output from an
ideal HAWT is proportional to the blade- or swept-area and the wind
speed cubed). To overcome these issues, various attempts have been
made in prior art to measure wind using other than mechanical
rotational devices.
Active remote sensing technologies (SoDAR and LiDAR): Sonic
detection and ranging (SoDAR) and light detection and ranging
(LiDAR) are two so-called active remote sensing technologies that
rely on sound (pulsed acoustic energy) and light (pulsed laser
light), respectively, to measure wind profiles. These, typically
ground-based, systems generally operate by emitting sound and light
pulses vertically at known intervals and then determining wind
direction and speed by measuring both the intensity and the
frequency (Doppler shift) of the back-scattered (reflected) sound
in the case of the SoDAR and back-scattered light (from airborne
sub-micro-particles) in the case of the LiDAR. Wind profiles at
various heights (up to hundreds of meters) may be obtained by
analysing the return signal at a series of times following the
transmission of either sound or light pulses (the return signals
recorded at any particular delay interval will provide
three-dimensional wind profile data for a height that can be
calculated based on the speed of sound and light respectively).
While active remote sensing technologies offer some distinct
advantages over in-situ mechanical anemometers, there are several
drawbacks, not least of which are cost, size and complexity.
Another consideration is that remote sensing technologies typically
provide mean data only, as data on standard deviations (e.g.
wind-speed, -direction and -gust), are usually either not available
or unreliable. This is because remotely sensed values are more
likely to be averages over some volume that is related to a beam
width or pulse length, whereas in-situ sensors--such as cup
anemometers--sample instantaneously at a known point in time and
space (point-measurements). In addition, the signal processing
algorithms for acoustic systems require extensive filtering to
ensure a good signal-to-noise measurement because SoDAR performance
is adversely affected by environmental noise pollution and
reflections of the pulse from ground obstacles (ground clutter).
LiDAR system performance is equally inhibited in heavy fog, cloud,
and other conditions with high aerosol concentration. Perhaps most
significantly, is the fact that both SoDAR and LiDAR applications
generally do not report valid data during periods of snow, strong
winds, and heavy rain which, in turn, mitigates against their sole
deployment in extended wind trials such as those required for wind
farm site assessments. According to an independently written report
from the World Meteorological Organisation the differences between
remotely sensed and point measurements can cause ` . . . problems
with comparison, interpretation and validation of data, and their
use in models, and with continuity of historical records` (P.
1)--See Kadygrov, E. N. (2006) World Meteorological Organisation:
Instruments and Observing Methods Report No. 89--Operational
aspects of different ground-based remote sensing observing
techniques for vertical profiling of temperature, wind, humidity
and cloud structure: A Review, WMO/TD-No. 1309.
Hot-wire anemometry: The hot-wire anemometer is, essentially, a
thermal anemometer. The measuring principle is based on the
relationship between the electrical resistance of the fine wire
that is used (e.g. tungsten) and the flow speed of a passing fluid
(e.g. air). As wind passes over the electrically heated wire it
tends to cool by way of convective heat transfer thus changing the
resistance of the wire conductor by an amount that is proportionate
to wind velocity. In other words, the heat loss to fluid convection
is a function of the fluid velocity. With the capability of high
frequency-response and fine spatial resolution, hot-wire anemometry
is particularly useful for measuring turbulent flows, or any flow
within which rapid velocity fluctuations are of interest. The
limitations of this technology are that the instruments are
orientation sensitive and in isolation cannot determine wind
direction. The devices are also unsuitable for industrial
deployment as the thinness of the wire normally used is highly
susceptible to damage. The device is also prone to malfunction in
so-called "dirty flows" wherein accumulated debris on the wire
conductor can change the resistance, as can any form of natural
precipitation.
Sonic anemometry: Sonic anemometry operates on the principle that
the time required for a sound wave to travel (between paired sonic
transducers located at a known fixed distance apart) is effected in
a way that is proportionate to the wind speed that passes through
the gap between the transducers. Pairs of sonic transducers may be
further combined to yield a measurement of fluid velocity in one-,
two- and three-dimensional flow. As with hot-wire anemometry the
high frequency-response of these devices, along with fine spatial
resolution, make sonic anemometers useful for measuring turbulent
flows. The disadvantages are that these instruments are known to be
adversely affected by environmental noise pollution of any sort. In
a further limitation, it has found that when the sonic transducers
become coated with water (even in light precipitation, or are
struck by large raindrops, the output is severely compromised. One
of the main drawbacks of this instrument, however, is the
distortion of normal flow (shadowing) characteristics caused by the
device's own housing arrangement for the transducers. A procedure
known as "shadow correction" is required to be performed in a
wind-tunnel facility which creates a "look-up" table of correction
factors to be applied so as to adjust the wind speed output
according to its sensitivity to the particular off-angle position
from the incoming flow stream.
Pitot-tube anemometry: The concept of measuring fluid flow velocity
using a simple tube arrangement is known in prior art since at
least the early 18th century and operates on the known principle
that a moving fluid exerts pressure on any object placed in its
path. The basic Pitot Tube--so-called after the inventor Henri
Pitot--comprises a straight tube, sealed at one end, with the open
end oriented directly into the fluid flow. As the tube itself will
contain the fluid within which it is immersed, a pressure can be
measured (the moving fluid is brought to rest, it stagnates, within
the tube as there is no outlet to allow flow to continue). This
pressure is the "stagnation pressure" of the fluid and the point at
which the dynamic flow meets the standing fluid is known as the
"stagnation point". If the stagnation pressure can be determined
and the static pressure is a known quantity, and the enveloping
fluid may be classified as incompressible (e.g. air or water), then
Bernoulli's Equation may be applied to determine point measurements
in the fluid velocity. The simple pitot-tube (and its variants)
continues to be used on aircraft to measure airspeed; in marine
applications to measure the speed of a vessel through water; and,
in various industrial applications to measure the local velocity at
a given point in space and time in the flow-stream of any given
fluid (e.g. in gas pipes and air ducts). The family of devices
known under the general category of pitot-tube anemometers may be
further subdivided into two discreet subtypes: Multi-Hole Pressure
Probes (MHPs) and Multi-Tube Pressure Probes (MTPs).
Multi-Hole Pressure Probes (MHPs) are a derivation of the
pitot-tube concept. However, the principle of measurement used with
MHP technology is somewhat different and is based on taking
pressure measurements at distinct points on the surface of a bluff
body immersed in a fluid stream. The contour of the bluff body and
the positioning of the pressure ports are therefore critical
computation elements requiring careful selection, positioning and
calibration--in practice the calibration procedure tend to be
experimental as opposed to analytical. Conventional MHPs comprise
several small diameter tubes axisymetrically arranged inside a
larger tube with one end machined into the shape of the so-called
"probe" or "tip" of the MHP. Many different tip (or probe) shapes
have been deployed in MHP technology including spherical, conical,
faceted and cylindrical surfaces. The known relative position of
each pressure port on the surface of the bluff body (i.e. the probe
tip) allows calculation of both a flow direction and a flow
magnitude. A three-hole probe is capable of measuring a single flow
angle--that is, measuring a two dimensional flow. Five and
seven-hole probes are capable of determining two flow
angles--allowing a fully three dimensional velocity field to be
measured. The two additional holes allow seven-hole probes to
measure higher angles of attack in the order of 150.degree. (the
so-called cone angle) than five-hole probes.
U.S. Pat. No. 5,929,331 (Kinser, R. E. and Rediniotis, O.K.),
discloses a multi-directional velocity measurement probe with
eighteen ports purportedly extending the measurable range of
velocity inclinations to a cone angle in the order of about
340.degree.. In Kinser, the body of the probe tip intrudes into the
flow stream. At the probe tip, there is internal micro-machining of
the probe tip to allow for separate measurement points about the
probe tip. In this context, it is to be noted that the suggested
tip or probe diameter is 6.14 mm. It will be appreciated that
micro-machining this is complex, expensive and generally
impractical to manufacture in the suggested configuration.
Furthermore, and as a function of the operating principle of MHP
technology, it has been shown that any imperfections whatsoever on
the surface of the probe tip, such as slight indentations, burrs,
scratches or adherences has the potential to severely compromise
the flow data produced by the instrument.
Eckman, R. M, et al., A Pressure-Sphere Anemometer for Measuring
Turbulence and Fluxes in Hurricanes, Journal of Atmospheric and
Oceanic Technology 2007; 24: 994-1007 disclose a further derivation
of MHP technology specifically for use in measuring the extreme
wind turbulence encountered in tropical cyclones. Therein is
described an experimental instrument called the Extreme Turbulence
(ET) probe, which the authors further describe as a
"pressure-sphere anemometer". In Eckman, the probe tip comprises a
43 cm diameter polished fibreglass sphere (divided into two
hemispheres split along a vertical seam), with three rows of
pressure ports running horizontally around the sphere. Within each
row, the ports are situated at 36.degree. apart yielding a total of
30 pressure ports on the surface of the probe. Each of the 30
external ports is connected via plastic tubing to an array of
individual, PCB mounted, analogue pressure sensors located within
the sphere (a data acquisition module, positioned below this PCB,
receives analogue input from the board-mounted sensors via a 26-pin
ribbon cable and outputs the digitised data through a USB cable).
In general operation, the ET system must first locate the pressure
port closest to the velocity stagnation point of the sphere:
pressure measurements, provided by the ports nearest the stagnation
point, are then used to compute the three-dimensional velocity
vector.
The first ET probes were built using "pinhole ports" of 1 mm
diameter so as to provide minimal disruption of the spherical
surface of the probe tip (and to maximise the space inside the
sphere by using small diameter pressure tubing to connect to the
sensors). However, field tests showed that when raindrops strike a
pinhole port, the pressure sensor registered large transient spikes
in the output data (causing the acquisition software to misidentify
the location of the stagnation point on the sphere). In a second
aspect, the pinhole ports were enlarged to 6.4 mm in diameter.
This, in turn, caused a problem with water ingress fouling the port
sensors which was resolved by arranging the now larger connecting
tubes in such a way as to provide gravity drainage to prevent water
from entering the device (an active defence mechanism involving
continuous pneumatic back-flushing was considered and rejected by
the authors in favour of this passive drainage system). Increasing
the diameter of the port causes other issues not considered
pertinent by the authors, interested as they are, in
hurricane-force winds only. The issue is that data contamination
may occur, most especially at lower wind speeds, due to the fact
that the pressure ports themselves can act as vortex generators,
triggering an earlier transition to turbulent flow. However, the
main limitation of this device is that--like other pressure
spheres--it does not function well at low airspeeds (i.e. low
relative to cyclonic air speeds). Field trials with the ET probe
indicated that velocity measurements increasingly drop out once
airspeeds fall below roughly eight meters per second i.e. when the
dynamic pressure is at about forty Pascal.
The prior art is replete with examples of MHP technology adapted
specifically for wind measurement. For example, U.S. Pat. No.
2,701,474 (Goudy, P. R.) issued Feb. 8, 1955 (see FIG. 10),
describes a multiple pressure tube arrangement for the measurement
of wind direction and velocity. What is described in the patent is,
in effect, a precursor to present day MHP technology. Therein, the
bluff body of the probe comprises a substantially flat Pitot probe
head, shaped as two very flat truncated cones joined by a short
cylindrical surface at the larger diameter. Two pairs of oppositely
faced pressure ports, spaced in quadrature, are located on the
surface of the cylindrical midsection with an angular separation of
90.degree..
In another example, Japanese Patent Application JP57100352 A,
published Jun. 22, 1982, discloses a probe head in the shape of
disc-type hollow case, rounded at the perimeter to attenuate flow
disturbance. Dynamic or total pressure ports (8 in number) are
positioned coplanar on the curved surface of the disc-type probe at
an angular separation of 45.degree.; UK Patent Application
GB2379026 A (Read, F. E.), published Feb. 26, 2003, discloses a
similar multiple pitot-tube arrangement comprising a hollow
disc-like body (or probe) having a cylindrical peripheral wall with
up to sixteen counter-sunk pressure ports (described as holes
flared out towards the outer surface of the peripheral wall)
positioned coplanar around a vertical axis at an angular separation
of 22.5.degree.. The positioning of the pressure port openings on
the outer surface of these various shaped probe heads leaves these
particular devices prone to the same limitations as the pressure
sphere anemometer previously described (see Eckman et al., para.
230-235 above). Furthermore, in each of the cases described, the
coplanar positioning of pressure ports around a vertical axis,
limits these devices to measuring the horizontal component only of
wind speed and direction. A further example of such a construction
is that of U.S. Pat. No. 5,929,331, which has a spherical probe
head with a plurality of ports openings on the surface at which
pressure is measured.
Multi-tube pressure probes (MTPs): Various attempts have been made
in the prior art to develop a method of measuring wind speed and
direction utilising multiple pitot-tube arrangements. What
distinguishes this prior art from MHP applications is a common
design feature including a plurality of pitot tubes positioned
equiangularly over 360.degree. and extending outwards
horizontally-coplanar from a vertical central axis directly into
the free flow stream. Typically, the pitot-tubes are, in turn,
connected to individual differential pressure transducers via
pressure tubing of various material types, lengths and diameters.
The pressure transducers convert the dynamic pressure signal from
the pitot-tubes into an electrical (analogue) signal which is
further typically routed to a signal conditioner/amplifier and,
further to an analogue-to-digital (A2D) converter for signal
conversion. The digital output data is then routed for further
processing/filtering of the data, oftentimes using bespoke
algorithms.
An example in the prior art of a device using these design
principles is described in International Patent No. WO2007/042803
A1 (Shields, J. A.), issued Apr. 19, 2007. This patent discloses an
instrument for determining the horizontal speed and direction of
movement of a fluid relative to a body, said device comprising a
plurality of pitot-tubes or probes, arranged at a fixed annular
separation in a common horizontal plane and aligned with a common
central axis. The pitot-tubes (numbering 5 at 72.degree. annular
separation) are connected to individual analogue output pressure
sensors via lengths of plastic tubing (so-called "connection
pipes") up to 10 meters in length (in Shields, the bank of pressure
transducers and the so-called "algorithm unit" are located remotely
from the probe tip itself).
Variations on a theme similar to that described by Shields (2007)
have been described in prior art: US Patent Application No.
2005/0005695 A1 (Corey, H. S. and Lane, B.), issued Jan. 13, 2005
which describes a differential pressure wind meter, comprising a
plurality of pitot-tubes (six in number at 60.degree. angular
separation) aligned horizontally coplanar within a lobed housing,
each connected to individual micro-electro-mechanical (MEM)
differential pressure sensors via lengths of tubing; and
subsequently described in, Chinese Patent No. CN202075303 U
(Huiqiang Tang et al.,) published Dec. 14, 2011, comprising four,
rather than five, mutually perpendicular pitot-tubes arranged
horizontally around a vertical central axis (connected to four
matched differential pressure sensors).
Although not specifically wind related: European Patent Application
No. EP0947809 A2 (Mostardi-Platt) published Jun. 6, 1999, discloses
a method and apparatus for measuring a cross section of gas flow in
a conduit such as a stack or duct. This specification describes
using a plurality of a variation of the basic pitot-tube known as
s-type pitot-tubes (16 in number) arranged in a coplanar
configuration oriented to the incident flow stream in a conduit.
The stated object of this latter device is to monitor and indicate
flow measurements at a cross-section in the normally unidirectional
flow encountered in a conduit such as an emission stack or
duct.
Thus configured, the output from these various MTP devices simply
attempt to mimic the data output expected of mechanical cup
anemometers and wind vanes, and are thus incapable of providing the
three-dimensional flow profile data so needed by the wind and other
industry sectors. Furthermore, said devices cannot account
sufficiently for wind shear and/or wind flow inclination, vertical
wind vectors and wind turbulence characteristics.
The use of devices of the type very generally described above has
not been restricted to measuring wind speed and in this respect
US2014/0130608 is an unusual example where a small number of pitot
tubes are arranged inside a sphere with the openings of the pitot
tube being at the surface of the sphere. The device is unusual in
that it is for measuring the speed and direction of a diver's
movements and hence the position of the diver when underwater.
SUMMARY
What is evident from the review of the foregoing prior art is that
there is a number of problems in the art. The present application
is directed at providing a robust measurement device capable of
providing a plurality of reliable point-measurements in three
dimensions. The instrument described herein is able to measure wind
shear and/or wind flow inclination, vertical wind vectors and wind
turbulence characteristics.
Moreover, and whereas conventional mechanical anemometers are
somewhat adequate for measuring mean wind speeds, there is a
general need for a device capable of following and recording the
higher frequency wind fluctuations that are ever-present in
real-world situations and capable too of measuring directly the
input quantity of interest i.e. the dynamic pressure.
Advantageously, the present application provides an instrument that
can measure these and indeed offers a number of further
advantages.
Accordingly, the present application provides a FVMD instrument in
accordance with the claims which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
To facilitate a more complete understanding of the present
application and its technical and commercial advantages, attention
is drawn to the detailed description of the initial preferred
aspect which may be interpreted by referring to the accompanying
drawings, in which:
FIG. 1 is a pictorial representation of an FVMD instrument in
accordance with an exemplary aspect of the present application;
FIG. 2 is an exploded view of an exemplary Higher Level Assembly of
the FVMD instrument of FIG. 1;
FIG. 3 is a schematic arrangement of the pitot-tube assembly of the
exemplary instrument of FIG. 1; and
FIG. 4 shows the arrangement of an exemplary Control &
Acquisition Module for use in the instrument of FIG. 1.
DETAILED DESCRIPTION OF THE APPLICATION
The present application provides a multi-directional fluid velocity
measurement device which is suitable for measuring three
dimensional characteristics of fluid flow and is particularly
suited to measuring air flow. It will be appreciated in the context
of the description which follows that by three dimensional is meant
that the fluid velocity is measured about three orthogonal axis (x,
y and z) rather about a single plane defined by two axis (x,y). It
will be appreciated from the description that follows that there a
number of different features, some of which provide an advantage on
their own and others which provide an advantage in combination with
one or more other features. Each of these advantages is to be taken
as being separate and divisible from the others with the result
that only those features necessary to provide an individual
advantage may be employed in a FVMD.
In general terms, the device comprises a main body. The main body
functions as a support for a plurality of Pitot tubes. The main
body is suitably substantially spherical in nature, i.e. the outer
surface of the main body is substantially spherical.
The main body may also function as a housing for sensors and
associated electronics. The main body may also house a power
source, e.g. a battery or battery pack, for powering the sensors
and associated electronics. The main body may be pneumatically
sealed to the atmosphere. At the same time, the main body may be
formed from or coated in a plastics material to reduce the effects
of exposure to the atmosphere, e.g. corrosion.
To facilitate access to the inside of the main body, the main body
may be formed as two separate hemispheres. The hemispheres are
suitably configured to engage with each other. Thus, for example,
the hemispheres may have co-operating flanges that overlap and
engage with one and other allowing for a friction fit between the
hemispheres. A locking feature, e.g. locking nut or similar feature
may be provided to lock the hemispheres together.
The main body is supported by a support structure. The support
structure may for example be a pole. A support engaging feature may
be provided on the main body for removably engaging with the
support structure. Suitably the support engaging feature is
provided at the bottom of the main body. A locking feature may be
provided to lock the support engaging feature to the support
structure. The support structure and engaging feature may also be
configured to provide a power and/or data connection to the
associated electronics within the main body.
The plurality of Pitot tubes extend from the surface of the main
body. Each Pitot tube has a proximal end which engages with the
main body and a distal end remote from the main body. The effective
length of the Pitot tube, which may be taken as the distance
between the distal end and the proximal end is suitably selected so
that the distal end (measurement point) of the Pitot tube is a
sufficient distance from the outer surface of the main body such
that the pressure readings taken by the Pitot tubes are not
substantially corrupted by the localized pressure variations
created by the wind flowing over the main body.
More specifically, the sufficient distance should be selected to
correspond at least to the radius of the main body. More desirably,
the distance is at least twice the radius of the main body. At the
same time, it is desirable to limit the distance so that there is
not a significant distance between the ends of pairs of Pitot tubes
arranged opposite each other about the spherical main body so as to
minimise temporal and spatial variations in measurement.
Accordingly, the sufficient distance should be selected to be less
than ten times the radius of the main body.
At the same time, the Pitot tubes and housing may be designed to
co-operate together to minimise air flow distortion.
Thus the shape of the main body may be shaped at the interface to
the Pitot tubes to present a continuous curved surface to air flow
rather than the Pitot tube external surface joining the connecting
main body surface at an abrupt angle of 90.degree..
Each of the Pitot tubes has a measurement port provided at its
distal end. The measurement port is in fluid communication with an
opening at the proximal end of the Pitot tube, which in turn is in
fluid communication with a respective pressure sensor.
The Pitot tubes are arranged in a 3D configuration/pattern about
the main body. Thus the overall arrangement of the Pitot tubes is
not co-planar. The arrangement of Pitot tubes in a 3D configuration
allows for the measurement of fluid flow in 3 dimensions.
Advantageously, the 3D configuration allows for the measurement of
one or more of: wind shear, wind flow inclination, vertical wind
vectors and wind turbulence characteristics. The number of Pitot
tubes is suitably selected to be more than is actually required to
present a reasonable 3D measurement. The advantage of this is that
the system has inherent redundancy. Accordingly, the failure of a
measurement from any Pitot tube (e.g. by blockage) or associated
sensor will have a minimal impact on the overall quality of the
data output from the instrument. Such a feature is of great utility
given the likely desire to position some devices at heights up to
and exceeding 100 m for example on meteorological mast
installations.
It is appreciated that the FMVD instrument is not intended to be
hand held and in fact in the form shown is a relatively large
device compared for example to a hand-held anemometer. For example,
the radius of the main body may be of the order of 5 to 20 cm. At
the same time, the instrument will probably be making measurements
at a quite a distance from the ground, e.g. 100 meters above the
ground. It may also be used for extended periods of time of the
order of months.
Accordingly, ensuring the device is easy to install and reliable in
use is important. In one aspect, this inherently provided by
avoiding the use of moving parts (as found for example in cup
anemometers and wind vanes).
The device provides for this by providing the device in modular
form, for example the two-hemisphere construction of the main body.
At the same time, the Pitot tubes and main body are removeably
engageable with one and other. More specifically, the main body
provides a plurality of sockets in the outer surface. Each of the
sockets is configured for engagement with the proximal end of a
Pitot tube. The sockets may be proud of the outer surface in which
case they may be shaped to minimise disruption to the air flow
about the main body. The advantage of shaping (in a curve) the
effective interface between the Pitot tube and main body is that
the required length of Pitot tube may be reduced.
Having the Pitot tubes removable allows for a faulty/blocked Pitot
tube to be replaced in situ without replacing the entire
instrument. Equally, it allows for the installation and alignment
of the main body at a site and the subsequent addition of the Pitot
tubes. The socket to Pitot tube connection may be a screw fit to
ensure a reliable connection. Although other configurations are
possible including push fit or a push and twist lock fit. In any
event, the connection is preferably selected to allow for the
removal/installation of the Pitot tubes by hand to avoid the need
for the use of tools at height. The opposite side of each socket to
the Pitot tube is in fluid communication with a pressure sensor.
Thus in one configuration, the sensor is integrated with the socket
and in another configuration the sensor is connected to the socket
by means of a flexible tube or similar structure.
A further advantage of having removable Pitot tubes is that it
uniquely provides the user with the flexibility to change, with
considerable ease, the nose-profile of each of the pitot-tubes (and
for example to thereby change the overall dynamic response
characteristics of the instrument).
At the same time, as the instrument is intended for use in all
environmental conditions, certain measures may be provided to
protect the instrument from the environment and in particular the
features of snow and ice. It will be appreciated that the
associated electronics within the main body will generate heat
which in itself may be sufficient to prevent freezing on the outer
surface of the main body. However, in the event that this is not
the case, one or more electrical heating elements may be provided
about the surface of the main body. A thermostat may be provided
within the housing (e.g. as part of the associated electronics) to
operate the heating elements where the temperature of the air or
surface of the main body drops below a threshold temperature.
Similarly, Pitot tubes may be provided with a heating element to
prevent their freezing. An electrical connection may be provided to
these heating elements by electrical contacts provided in or about
the sockets which engage with corresponding electrical contacts on
the Pitot tube. Using heating elements, the instrument can
reasonably be expected to withstand ambient temperatures within a
range of .+-.40.degree. C. The heating elements may be in the form
of a self-regulating tape or cable which may be moulded in the
housing or Pitot tubs. An example of such a self-regulating cable
is FREEZSTOP.TM. which is available from OEM Heaters of
Minneapolis, USA (www.oemheaters.com).
Additionally, or in place to the heating elements, the external
surface of the main body or the pitot-tubes or both may be treated
using a hydrophobic coating to repel water including
precipitation.
The pressure sensors are suitably low pressure digital transducers
which provide a digital output rather than analogue output signals
thereby eliminating the need for expensive signal
conditioning/amplification and A2D conversion technology.
Deployment of such sensors has the added benefit of streamlining
the data acquisition process thus avoiding any possible error
accumulation associated with signal conditioning, amplification,
conversion and/or calibration circuitry. The use of such
transducers allows for housing the sensors within a smaller main
body, which means that the pressure transducers may be located in
as close a physical proximity as possible to the input quantity of
interest so as to avoid any phase lag with respect to the true
pressures at the dynamic pressure points of the various
pitot-tubes.
At the same time, the main body may be employed to house the
associated electronics. These electronics allow for capturing
real-time fluid flow profiles in three dimensions, i.e. as obtained
from measurements from the pressure sensors. The electronics may be
configured to provide direct and instantaneous data output on flow
speed, flow inclination, shear, and turbulence characteristics.
With the arrangement of Pitot tubes, this provides for a capture-
or cone-angle as near as practicable to 360.degree.. The
electronics may also be used to detect blocked or otherwise faulty
Pitot tubes by analysing the data for inconsistent measurements.
Where a blocked tube is identified, the system may address it in a
number of different ways. In a first approach, the system may
simply send a message to a supervising system/user informing of the
blocked tube and in response to which a user can be dispatched to
replace/unblock the tube. In a second, the system may turn on a LED
or other indicator (not shown) on the surface of the spherical
housing adjacent to the blocked tube to indicate to a user that a
blocked tube has been detected and to identify the blocked
tube.
In another approach, a back wash\flush feature may be provided
allowing a source of pressurised gas to be connected to the
proximal end of the Pitot tube to block out the blockage from the
tube. In general terms, the source of pressurised gas may be housed
remote from the housing, e.g. a CO.sub.2 or compressed air cylinder
and connected by a flexible pipe to the spherical housing. At the
same time, a valve connection (operable by the electronics) may be
provided to connect the source of pressurised gas to the Pitot
tube. To prevent damage to the sensors the valve connection may at
the same time as connecting the pressurised air to the Pitot tube
disconnect the sensor from the tube. It will be appreciated that
the back flush feature may be used periodically (i.e. to prevent a
blockage building up) or in response to the detection of a blockage
or a combination of the two.
The electronics may include a data recorder comprising a processor
and associated memory. The memory allows for the recording of
measurements. The size and nature of the memory may be selected
based on the measurement duration intended and whether a data
connection is available or not to off-load recorded measurements.
An interface is suitably provided to allow the processor acquire
measurements from each of the pressure sensors. At the same time,
the electronics may include one or more communications modules to
facilitate sending measurements to systems remote from the
instrument. Thus, the electronics may include a real-time
processor, a user-programmable FPGA, and built-in I/O capability
and peripherals such as, for example, USB, RS232, RS485, CAN, SD,
and Ethernet connectivity. The Ethernet connectivity may be by
means of a wireless (e.g. WiFi.TM.) connection or by means of a
wired (e.g. Ethernet) cable. Equally, other forms of communication
may be provided included for example, GSM, GPRS, 3G or 4G mobile
phone connections. Additionally, the electronics may include an
interface for one or more environmental sensors including for
example measuring one or more of temperature, humidity, barometric
pressure and rainfall. It will be appreciated that certain of these
sensors may be provided on the main body and that others may be
positioned a distance therefrom to avoid interfering with the
airflow around the housing, in which case the interface may be
wired or wireless. The advantage of using an Ethernet cable is that
POE (power over Ethernet) may be used to provide power to the
electronics.
Other sensors may be connect It may also incorporate
three-dimensional accelometry, gyroscopy or magnetometry sensors.
These allow for the orientation of the instrument to the ground to
be determined. The electronics may also include for example a GPS
receiver to allow an accurate determination of the position of the
instrument.
The added advantage of such an arrangement is the elimination of
the associated cost and complexity of design commensurate with the
routing of long lengths of pressure tubing through the instrument
to a remote data acquisition module as is described in the prior
art.
A power source, e.g. battery or battery pack, may be housed within
the main housing. A power connection may be made to the main
housing (for example through the support) in place of or addition
to the power source.
The present application will now be described with reference to an
exemplary construction employing a configuration of 64 Pitot tubes
which is illustrated in FIGS. 1 through 4.
FIG. 1 depicts a general view of the assembled FVMD instrument in
accordance with an exemplary first aspect of the present
application. The instrument comprises a central support sphere 102
with 64 pitot-tubes 104 positioned around the surface of the
central support-sphere. The central support sphere is formed as two
parts: a top-hemisphere 106 and a bottom-hemisphere 108. Suitably,
a seal is provided between the top and bottom hemispheres to
pneumatically seal the interior to the atmosphere. The seal may for
example be an O-ring 110. At the same time one or more locking
features 112 may be provided to keep the two spheres together.
Depending on the application, it will be appreciated that the
pattern of Pitot tubes may be varied. Thus, for example, in a
situation where there is a generally horizontal laminar airflow,
the pattern of Pitot tubes may be positioned close to the equator
(in geographical terms) of the spheres with a set of Pitot tubes
about the equator and one of more sets of Pitot tubes arranged at a
latitude above and/or below the equator, for example at 15.degree.
above/below the equator. In contrast, where the application is
measuring downdraft at an airport, a Pitot tube may be located at
the North Pole of the sphere with a further set of Pitot tubes
arranged at latitude of 15.degree. below the North Pole.
In the exemplary pattern shown, the positioning of the pitot-tubes
around the central support-sphere is based on an application of
recursive zonal equal area partitioning of the sphere into 65
separate regions, with 64 pitot-tubes located normal to the surface
of the sphere in the centre of each region (the bottommost zonal
partition/region is left free for the mounting arrangement,
comprising a support 114 which engages with an opening 118 in the
bottom of the bottom hemisphere and which is locked in place by
means of a locking bolt 116 or similar). As mentioned above, it
will be appreciated that the dispersion pattern of the pitot-tubes
on the surface of the sphere is application-specific and may be in
any variety of configurations, for example at the 20 vertices of a
dodecahedron.
Within the hemispheres, a central support structure 120 is provided
which in turn is used to house the electronic circuitry. As shown
in the exemplary construction of FIG. 4, the support structure
comprises a top housing 200, a bottom housing 208, a left side
housing 212, a right side housing 204 and a faceplate 206 which
co-operate together to house electronic circuitry 210.
In general operation, once the device is placed in a flow stream,
individual pressure signals are continuously received at the distal
points of each of the pitot-tubes. These pressure signals propagate
at a known speed through the pitot-tubes which are, in turn,
connected to individual micro-electro-mechanical (MEM) low pressure
sensors/transducers. The totality of the readings from the sensors
provides a differential pressure output which--by way of an
application of the Bernoullian Equation--may be converted to a
fluid velocity output that is typically expressed in either
analogue or digitally-encoded format or both. It will be
appreciated that this form of pressure signal conversion may be
effected using a custom differential MEM; a gage pressure MEM; or
two individual and separate MEMs, one for measuring static
(barometric) pressure and the other, dynamic pressure. Exemplary
MEMs would include, but are not limited to, strain gauge,
capacitive and piezoelectric types. The mean fluid velocity (or
vector) will generally be indicated by the pitot-tube returning the
highest pressure reading (hereafter the incident tube). Although,
it will be appreciated, that even greater directional accuracy may
be computed by triangulating the true pressure vector by including
in the calculation the pressure readings not only from the incident
tube but also the (lesser output) readings from the surrounding
tubes. It will also be appreciated that the greater the number of
individual pressure readings the higher the resolution of the data
that is produced.
Specifically, a variation of a multiple-point interpolation
algorithm is employed in the present application which begins with
the identification of the pressure readings from each of the pitot
tubes. A selection of adjacent windward facing pitot-tubes is then
made, based on the pressure relative to the maximum measured
pressure, and a proscribed minimum detectable pressure. Once this
stage in the algorithm is reached, the approximate direction of the
incident wind is then calculated as the weighted average
orientation of the selected tubes, using the pressure values as the
weight factor. At this point, the attack angle of the calculated
approximate wind direction is calculated for each selected
pitot-tube. The approximate dynamic pressure at the device is
calculated using a linear fit of the measured pressures to the
known angular response profile of the pitot-tubes. The actual
dynamic pressure, and wind direction, are then calculated using a
non-linear least squares fit of the measured pressures to the known
angular response profile of the pitot-tubes, using the approximated
values (as calculated above) as the seed values. The density of the
air is applied to the calculation and is calculated using the
measured values of air temperature and relative humidity from the
externally mounted sensors. The wind speed is then determined from
Bernoulli's Equation using the dynamic pressure calculated above,
the static pressure sensed by the inward facing port on the
transducer, and the density of the air.
Each pitot-tube assembly, as shown in the exemplary construction of
FIG. 3, is designed such that each pitot-tube 104 is easily
removable and replaceable for ease of maintenance (or change of
application). The custom formed thread on each pitot-tube is
intended to co-operate with a respective socket 122 on one of the
hemispheres. Thus a Pitot tube may be screwed into a socket. The
Pitot tube is suitable formed with a shoulder recess 130. This
shoulder recess is employed to retain an O-ring 123 which in turn
ensures a pressure seal between the Pitot tube and a corresponding
socket on the support hemisphere. The profile of each pitot-tube
and the matching protuberances (sockets) on the support hemispheres
are designed such that fluid flow distortion around the device is
minimised and the extension length of each tube is such that the
distal point of each intrudes into the free flow stream. As
discussed above, the nose-profile of the pitot-tube is somewhat
application-specific and that various nose-profiles may be deployed
each having its own particular measured angular response
characteristic. Examples of such nose-profiles would be familiar to
those skilled in the art but would include, for example but not
limited to, NPL, Cetiat and AMCA profiles.
The spigot-end of each pitot-tube, i.e. the extension of the
threaded portion, intrudes into the top and bottom support
hemispheres via the socket (capsule) recesses 130. A connection is
provided between the Pitot tube extension and a pressure sensor.
This may be by means of a flexible piece of tube. Alternatively, as
shown, the sensors are connected directly to the Pitot tube by
means of a Push-In Pneumatic connector 135 being shaped to receive
the extension of the Pitot tube and being connected by a short
section of flexible polyurethane tubing to a pressure
sensor\transducer 138.
Suitably, the pressure transducers deployed are of the
surface-mount or SMD variety. Each transducer may be individually
mounted onto a custom printed circuit board (PCB) 140 with a
right-angled 4-way header pin connector located on the underside of
the PCB to make connections to the electronics. A length of
polyurethane tubing is fixed onto the dynamic pressure port of each
transducer and sealed with a specialised 2-ear precision clamp 154
for a uniform compression seal. The trailing end of the
polyurethane tubing is further attached to a push-in pneumatic
connector 135. This sub-assembly is further enclosed in a
custom-designed two-piece capsule housing 151. The two-part capsule
housing 151 comprises a capsule upper 150 and a capsule lower 152.
The two-part housing acts both as a locator slide mechanism
engaging with the interior side of a socket and also providing a
moderate environmental seal. When this sub-assembly, including the
two-piece housing, is pushed through the interior side of a socket
(capsule recesses) in either the top or bottom hemispheres. Rails
160 on the sides of the housing engaged in corresponding slides 162
on the capsule recess ensure a snap-fit connection is made between
the pneumatic connector port and the spigot-end of each pitot-tube.
It will be appreciated that this is but one configuration of the
device. For example, a single or double-sided PCB with a plurality
of surface-mounted sensors connected via separate lengths of
polyurethane tubing to the spigot-end of the pitot-tubes may also
be deployed.
In the arrangement shown, a differential pressure output from each
individual transducer is set up to communicate with an
off-the-shelf reconfigurable embedded control and acquisition
system that consists of a real-time processor; a user-programmable
Field Programmable Gate Array (FPGA); built-in heat-sink; I/O and
USB, RS232, RS485, CAN, SD, peripherals and Ethernet port. These
electronics (i.e. a control and acquisition system module) are
housed in casing, which is shown in FIG. 4 as being formed from 5
parts which serves to both provide moderate environmental
protection and to suspend the device in a known position in the
approximate centre of the FVMD instrument.
The means of communication between the sensors and the control and
acquisition module may be by means of any suitable communication,
for example the I.sup.2C (Inter-Integrated Circuit) protocol.
I.sup.2C is an open source, serial, single-ended computer bus
protocol. The exemplary configuration employed in the current
application makes use of six separate I.sup.2C buses (4 with 11
sensors each and two with 10 sensors each) to transfer data to the
FPGA. It will be appreciated that the use of this method reduces
the wiring required between the electronics and the sensors since
multiple sensors may be connected to a single cable and thus a
single end connector made to the electronics. A seventh I.sup.2C
bus is included to provide data from the various externally mounted
sensors required to resolve Bernoulli's Equation (i.e. relative
humidity, atmospheric pressure and temperature). The individual
Capsule Assemblies are assembled into the unit such that no
sensor's immediate neighbour is on the same bus. Such a
configuration provides an element of built-in redundancy for the
FVMD instrument in that it prevents an entire area of the sphere
becoming inactive in the event of a single bus becoming
inactive.
In addition--on the seventh I.sup.2C bus--there is a
system-in-package sensor featuring 3D digital linear acceleration
sensing capability; 3D digital angular rate sensing; and, 3D
digital magnetic sensing. This inertial measurement unit (IMU)
sensor 180 is internally mounted in a known position within the
sphere and is (algorithmically) referenced to the distal locations
of each of the dynamic pressure points on the pitot-tubes such that
each distal point can be accurately located in space and time
regardless of the instrument's orientation to detectable magnetic
fields, and/or regardless of any vibration of the mounting boom or
deflection of the instrument howsoever caused. The inclusion of the
IMU sensor 118080 eliminates the need to manually align the FVMD
instrument with a reference orientation such as true north.
The construction of FIGS. 1 to 4 are presented in the context of
using the device outdoors. It will be appreciated that the
structure may also be employed indoors, for example for measuring
air flow, within a data centre or similar application. Where the
device is intended for interior use, it will be appreciated that a
smaller spherical body may be required to reduce the lengths of the
Pitot tubes and thus the overall size of the instrument. In this
context, certain functional aspects may be moved from within the
spherical body to reduce the size of the spherical body. For
example, the electronics section 120 may be relocated outside of
the body with the I.sup.2C connections been made to electronics
housed externally to the device, e.g. by wiring through a hollow
support 114. Similarly, the sensors may be removed from the housing
and connections, e.g. flexible tubing, used to connect the Pitot
tubes to the sensors remote from the spherical body again
potentially through a hollow support 114. It will equally be
appreciated that these techniques used indoors may also be employed
in an outdoor construction.
Whilst the device of the present application has been described in
the context of obtaining a three dimensional measurement of fluid
velocity and in more particularly a three dimensional measurement
of air velocity, the device may be modified for other purposes.
Accordingly, in one configuration, the pressure sensors within the
pitot tubes may be replaced with microphones so as to provide a
three dimensional acoustic measuring device with appropriate
changes made to the electronics to accommodate recording pressure
from the sound rather than pressure from the wind as such.
Accordingly, whilst such a device is not claimed below, the
application should be taken as extending to such a device and in
particular a device for measuring sound in three dimensions is
contemplated in accordance generally with the claims which follow
except that the pressure sensors are replaced by microphones.
It will be appreciated that such an arrangement presents advantages
in that the pitot tubes inherently receive sound from the direction
in which they are pointing and discriminate sounds coming from
different directions. This means that less expensive microphones
may be employed to capture the sound in contrast to existing
systems which use directional microphones configured in a 3
dimensional array. At the same time, the system has an advantage
that sensitive components such as the microphones, audio
electronics and data storage or analysis electronics are protected
within the body of the sphere or within the pitot tubes. This may
be useful in rugged environments or situations where it may be
difficult to protect a conventional microphone array. The external
surface of the sphere or pitot tubes or both may be covered in a
sound absorbing or insulating material. This ensures that the sound
reaching an individual microphone is limited to those arriving
in-line with the Pitot tube.
In addition the direction in which the sound is coming from may be
readily determined. In its simplest form, this may be achieved by
selecting the Pitot tube whose microphone records the highest sound
level and selecting the outward direction of the Pitot tube as
being in the direction from which the sound has come. For greater
accuracy, a cluster of measurements may be employed and the
direction of the sound obtained by triangulation. For example, by
selecting the readings from a cluster of microphones, for example
three, with the highest measured sound levels. Using the measured
sound levels from the cluster, a triangulation may be performed to
more accurately determine the direction from which a sound is
originating.
One application for this is that, the sound measurement system may
be integrated with a security system. In this arrangement, a
pre-determined noise threshold may be used as a security sensor.
Where the pre-determined noise threshold at one of the microphones
is exceeded, the security system is triggered. Whilst such a
security sensor would be known generally, an advantage of the
present system is that once a sound is detected its direction of
origin determined. Thereafter, the security system may be
configured to activate one or more cameras to record/transmit a
picture/video of the area identified by the detected direction of
origin. This may for example, be by means of switching on a camera
which is directed in the general direction from which the sound has
come. Alternatively, it comprise a robotic camera having one of
tilt or axis control or both and where the security system is
configured to control the camera to point in the direction from
which the sound has come.
The present application has been described here in connection with
certain preferred aspects which are intended as examples only.
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